When I started my first aquarium in Calgary my friends were always amazed that I had real plants in it. That made me feel really good for back in Brazil, where I got started in the hobby, aquarium keeping was very low-tech and aquarium keepers relied on live plants to help filter their water. Everyone had live plants in their tanks, and the stores did not carry plastic ones (or if they did, their price would have been prohibitively expensive given the import restrictions of the time). Something that was second nature to me in the past was now considered to signify a level of expertise.

Many years later I joined the Calgary Aquarium Society and heard of the HAP program and how some club members had their aquatic plants flower, and some had actually propagated their plants from seeds. I realised then that I wasn’t such a hot shot after all for keeping Amazon sword plants alive and growing Aponogeton plants from bulbs. It was quite humbling from me to hear from the HAP masters on their latest feats with their aquarium plants.

Let me assure you that most of the aquarium plants available today are capable of flowering. It is quite natural for them to do so, and they will do it in an artificial setting when conditions are right. Some flowers are very pretty, others are barely noticeable, but one thing I’ve noticed with many of them is their short life – sometimes as short as one day or less. If you know your plant is about to flower and you want to enter it for HAP points, make sure you have a spotter on call or be ready to take a picture

So what is the secret? I don’t have a formula for making my plants flower, but I’ve noticed a couple of things. First is light. Without proper lighting the plants don’t grow well, much less flower. There is a certain level in which the plants do well and grow. If your light intensity increases past this level your plants should flower and grow vigorously providing they are established and you don’t have an algae problem in the tank. Regular light and dark periods are important too. Some people claiming that their plants flower when the light period is increased (up to 14 hours). I find my plants flower in winter, when the aquarium gets a few hours of sunlight on the front pane. I don’t change the light period (it stays 12 hours) but the light intensity changes dramatically with the sunlight.

Another factor seems to be plant mass. I once let star grass (Heteranthera zosterifolia) grow out of control in a corner of one of my tanks. It formed a tangled mass of plants growing all the way to the surface and actually running along the surface for half their length. Then the growing tip of the plants bent upwards and grew out of the water, producing tougher leaves and two flower buds per tip. This went on for a couple of months (January and February) and there were blooms every day. The plants’ mass could simply be an indication of the plants’ health (and therefore their ability to flower) although there is some evidence that plants do better when there is a large number of the same species together.

The third factor is nutrition. It takes energy to produce the flowers, and with some plants you can actually control the amount of flowers with fertilizer. Water lilies are an example. They need root fertilizer to flower well.

So if there is a formula to make aquatic plants to flower it must be:

flowers = healthy plants + light of proper intensity and time + nutrients

It is important to note that the majority of aquatic plants produce aerial flowers, so the plant will either grow to the surface or it will send flower stems up to the surface. A deep tank may prevent you from getting flowers because of the water depth. In this case you can try lowering the water level. The other dimensions of the tank are not at all important, just make sure the plant is not cramped.

As I said earlier, most aquarium plants are capable of flowering. As with anything in life some things are easier than others, and some things are impossible. Ferns are not flowering plants so don't expect Java fern (Microsorium pterops) or water sprite (Ceratopteris thalictroides) to flower. The most they will do is produce spores under their leaves. On the other hand, some plants that one may not immediately think of as flowering plants in fact are. Hornwort (Ceratophyllum demersum), Cabomba, and duckweed (Lemna minor) are three examples.

Here are just some of the plants that have produced flowers for various CAS members:

In the pond: water lilies (Nymphaea spp.); water poppy (Hydrocleys nymphoides); arrowheads (Sagittaria spp.); frogbit (Hydrocharis morsus-ranae); umbrella palm/papyrus (Cyperus spp.).

In the aquarium: Vallisneria spp.; temple plant (Nomaphila stricta); Cryptocoryne affinis; Amazon swords (Echinodorus spp.); many of the Aponogeton species (including the Madagascar lace plant); hornwort (Ceratophyllum demersum); Anubias barteri.